1. Field of the Invention
The invention relates to a method for controlling transmitter power, the method employing a control element controlled by a control signal, sampling means for taking samples of a signal from the control element, and a detector in connection with the sampling means, an adder and a loop filter, the adder and loop filter forming a controller for receiving a signal which is transmitted by the detector and forms part of a feedback signal for controlling the control element.
2. Description of Related Art
The invention is more closely related to switching the power of transmitters employed in GSM and DCS base stations, in particular. Network operators require a 30 to 42 dB wide adjustment range for transmitters that are switched on, i.e. in the ON position. In this situation the maximum power of a DCS base station transmitter can be 46 dBm and that of a GSM base station transmitter 58 dBm. The GSM recommendations specify the power level below which the transmitter is switched off, i.e. in the OFF position. In the OFF position the power level is below -36 dBm. The switching time should be below 15 .mu.s with frequency hopping and below 30 .mu.s with no frequency hopping. In addition, it must be possible to switch the power on and off without causing harmful transients on adjacent RF channels. With the transmitter in the ON position, a range of 30 dB, within which continuous power control is possible, should be left below the employed power. The above means that the dynamic range of power switching has to be continuous. In practice, the dynamic range should be e.g. between 63 and 75 dB.
A method of controlling the power of a high-frequency power amplifier is previously known. In the method the high-frequency power amplifier is controlled from the ON state to the OFF state by turning on an RF switch between a voltage-controlled attenuator and the high-frequency power amplifier. The high-frequency power amplifier is controlled from the OFF state to the ON state by turning off the RF switch.
The dynamic range of the power control arrangement is increased by switching a signal off by RF switches, whereby a shift occurs to the OFF state. A parallel loop is switched to the control arrangement at the same time as the signal is switched off. The parallel loop will slightly compensate for the transient problems caused by the rapid fading of the signal to be detected. The prior art solution has become quite complex. Furthermore, the solution requires very precise timing of RF switch control signals. Still further, the feedback signal of the control arrangement is not completely continuous, but has shown dead zones.